The ankle joint's intended movements are only flexion, also called dorsal flexion, and extension, also called planar flexion. Flexion is movement of the superior surface of the foot toward the anterior surface of the leg. Extension is the reverse action. The two lower leg bones, the tibia and the fibula, join to form the top half of the ankle joint. The ankle is composed of seven bones known as the tarsal bones. One of these is the talus or ankle bone. The fibula and tibia are held tightly together by ligaments and form a mortice for reception of the talus. A relatively complex ligament system holds the ankle joint together. The tibiofibular joints include three separate articulations, namely, the inferior tibiofibular joint which is the articulation between the lateral malleolus and the tibia; the tibiofibular union which is the union of the shafts of the tibia and fibula by an interosseous membrane that consists of numerous short fibers which pass transversely from one articular surface to the other; and the superior tibiofibular articulation which is the articulation between the head of the fibia and the fibular facet of the tibia. Normal movements of these tibiofibular joints consist merely of gliding movements, which are passive in character in that they complement the movements of the ankle joint. Thus, during flexion of the ankle, the fibula tends to be displaced upward. During extension, it is displaced downward. These movements are normally resisted by the interosseous membrane.
The chief traumatic problem associated with the ankle is ankle sprain, usually involving either extreme inversion or extreme eversion. Eighty-five percent of all injuries of the ankle are inversion injuries, in which the foot is forced inward in relation to the leg. In eversion injuries, the foot is forced outward in relation to the leg.
During engagement in a particularly strenuous activity, such as sports, it is advisable to restrain the ankle and tibiofibular joints from movement other than flexion and extension, and to restrain that movement beyond normal limits.
Fracture of the lateral malleolus is a common injury resulting from either a blow from the medial side or sudden torsion. Both lateral and medial malleoli fractures usually result from severe twisting actions, such as those incurred in ski injuries, that cause a rotational shear of the joint. Such injury heals slowly. Protection should be provided to the healing malleoli in addition to local immobilization.